In the 3GPP, a standardization organization of communication standards, EPS is specified as a next generation mobile communication system (for example, see non-patent document 1). The EPS is composed of EPC (Evolved Packet Core) serving as a core network and a plurality of radio access networks which are connected to the EPC. Further, specific examples of the radio access networks are assumed to include not only radio access networks specified by the 3GPP (hereinafter referred to as a “3GPP access network”) such as E-UTRAN (Evolved-Universal Terrestrial Radio Access Network) and UTRAN (Universal Terrestrial Radio Access Network), but also radio access networks which are not specified by the 3GPP (hereinafter referred to as a “Non-3GPP access network”) such as WiMAX and wireless LAN (for example, IEEE802.11, etc.).
Additionally, a UE (User Equipment: mobile station) capable of being connected to these plurality of radio access networks is able to perform handover between radio access networks while maintaining communication session with the other communication end in accordance with a procedure specified in non-patent document 2, for example.
Further, non-patent document 3 discloses a new usage scenario that an individual radio access network has different characteristics in the aspects of maximum throughput, a cell radius or the like based on a radio access technology to be used, therefore, in view of the different characteristics, in an environment where a plurality of radio access networks are able to be used simultaneously, a radio access network for transmitting, for each application or the other communication end, communication data thereof (hereinafter referred to as a flow) is switched.
Specifically, in a flow unit, a quality of service to be required (real time communication, non-real time communication, a required band or the like) and a priority order of a radio access network to be used are set (hereinafter referred to as a policy), and when a higher priority radio access network has become available, a radio access network to be used is changed in a flow unit.
For example, a case or the like is shown in which, when a UE having a function of connecting to the E-UTRAN and the wireless LAN establishes two flows of VoIP (Voice over Internet Protocol) traffic and file download in an E-UTRAN area, and then moves into a wireless LAN area while being in the E-UTRAN area, in accordance with a policy which has been set, as to the VoIP traffic for which real time characteristics are required in terms of delay, fluctuation or the like, communication is continued via the E-UTRAN, and as to the file download for which real time characteristics are not required, switching is performed to the wireless LAN with which higher throughput is expected.